The present invention relates to techniques for communicating digital information, and more particularly to techniques for communicating digital information over a coded voice channel.
There is an increasing demand for advanced telephony services from customers, such as automated services that may be accessed and commanded by control sequences that are transmitted from a remote location. As a consequence, techniques have been developed for providing access to services from a communications network. In the world of wireless communication, ongoing work includes the development of a Wireless Application Protocol (WAP), which is a layered communication protocol that includes network layers (e.g., transport and session layers) as well as an application environment including a microbrowser, scripting, telephony value-added services and content formats. One part of WAP is the Telephony Value Added Services (TeleVAS), which is a secure way to access local functions like Call Control, Phonebook, Messaging and the like by means of a device independent interface to the underlying vendor specific operating system and telephony subsystem.
In fixed networks, techniques for providing access to services from a communications network have included the use of Intelligent Networks in which Service Access Points are nodes in the network that customers can access to obtain advanced services. It has also become common to access services at nodes that are independent of any traditional network operator. These nodes are implemented as service computers that can be connected in independent computer networks (e.g., the Internet) and accessed from at least one communications network (e.g., a telephony network or a mobile network such as the European standard Global System for Mobile Communication (GSM)). The communications network (e.g., a public telephony network or a mobile network) is then only utilized for establishing access to these independent computer networks. In order to keep the services provided by the network of service nodes independent of the traditional telecommunication networks, the access to a service node through such a telecommunications network can carry both data (e.g., speech) and control signaling on the same channel (i.e., in-band signaling can be applied).
In a cellular communications system, it is common for operators to offer a Short Message Service (SMS) for sending short messages to the cellular terminal. The messages are routed over a Short Message Service Center (SMS-C) server that stores and forwards the messages. The SMS service has several disadvantages with respect to the problem of exchanging control signals between a user terminal and a service node. For example, the SMS service does not render the sender any control of delays, and it provides no information about the status of the message. Furthermore, the pricing of the SMS service differs substantially from one operator to the next, with some operators keeping the price at a level that makes the service too expensive for many users. Another disadvantage is that various cellular network operators offer interfaces other than the SMS-C interface, from servers outside the cellular network, which means that it is cumbersome to send SMS messages to terminals belonging to different networks.
It is further known how to establish separate voice and data paths between two terminals through a plurality of telecommunication networks, one of which is a mobile network. However, the switching between the two modes is awkward and time consuming, which causes inconveniences to the user.
Whereas systems such as Internet Protocol (IP) communication can easily cope with mixed speech and data, this presents problems if the communication path includes a mobile network, such as a GSM network. More particularly, in this latter case the communication path includes a voice coder that is optimized for human speech and thus in-band modem signaling by means of, for example, tone frequencies (e.g., Dual Tone Multi-Frequency, or "DTMF") will result in a slow data rate at the risk of an increased error rate. A reason for this is that the character of a modem signal makes it less predictable than a voice signal. Known methods for managing these difficulties suffer from being impracticable from a user point of view or otherwise lead to technical solutions that are specific for each type of network involved. Further, future voice coders may behave even more unfavorably with respect to the ability to pass DTMF signals. Therefore, in-band signaling in communication paths comprising a plurality of networks, at least one including voice coding, is a problem to which an advantageous solution is needed.
The PCT Publication No. WO96/09708 by Hamalainen et al. ("Simultaneous Transmission of Speech and Data on a Mobile Communications System) describes how to use a voice channel over an air interface in a mobile system to transmit simultaneous voice and data, and in particular discloses a method and system whereby silent periods can be detected when no voice is present, thereby allowing the insertion of data into the transmitted frames. This publication further describes how the frames are completed with information bits in order to permit the separation of voice and data frames at the network side. A characteristic of the described solution is that it depends on the air interface protocol and that the means for separation of voice and data are integrated with the network. This solution is therefore not useful for solving the problem of simultaneous voice and data between a first mobile user terminal and a second service node that is external to and independent of the telecommunication networks involved in the speech path between the nodes.
It is further becoming common to adopt speech recognition methods for speech control of user services. A disadvantage with known methods is the need to "train" the speech recognition system to understand a specific vocabulary, language characteristics and even characteristics of the voice of the speaking person.